Rotary engines of the above mentioned type are comprised of an outer component having axially spaced end walls and a periphery curved or parallel to the axis and an inner component having axially spaced end surfaces and a periphery curved or parallel to the axis, which components hereafter for simplicity will be referred to as the housing and the rotor which housing defines a cavity having an epicyclic shape for a two apex rotor or in the shape of a two lobed epitrochoidal cavity housing for a three apex rotor.
Normally in such a rotary engine, there is an internal ring gear which is eccentrically mounted on the main crankshaft. The internal ring gear is fixed or secured within one side of the rotor and intermeshed to a pinion gear having a hollow shaft for free wheeling within the said main crankshaft. Particularly for a rotary engine with a three apex rotor the gearing ratio of the internal ring gear: pinion gear is fixed at 3:2 for which thereafter the pinion has to be fixed or secured to the housing frame. Such gearing ratio as mentioned above therefore will limit the diameter size of the main crankshaft due to the given eccentricity of such design.
Such fixing of the pinion as mentioned above to the housing frame kinematically will cause the power transmitted to be dependent on the strength of the cavity wall against the strong pressures of the rotor which receives the powerful impact as caused by the expanding gases soon after every ignition/combustion, particularly during extreme conditions when the engine is in operations. Sooner or later such conditions will cause an excessively heavy wear along the contact lines between the cavity wall and the rotor, which in the end will of course shorten the life or durability of the said engines.
Such rotor having axially spaced end surfaces and a peripheral wall parallel to the axis which hereafter for the purpose of simplicity will be referred to as the rotor with flat outer surface or flat rotor, will cause what is called "corner seal leakage" which is considered as one of the most serious problems to be solved due to is geometrical conditions.
By such limited size of the main crankshaft, fixing the pinion gear to the housing frame, and corner sealing, the whole performance of this typical rotary engine has been characterized by widely known, relatively low efficiency, high fuel consumption, high emissions, and excessive wearing etc.